1. Field of the Invention
The present invention relates to a process for hydrogenation of aromatic compounds such as the hydrogenation of benzene to cyclohexane and the supported nickel catalyst modified with up to 0.9 wt. % Cu therefor.
2. Related Information
Cyclohexane is the main precursor for the production of nylon products and as such, the demand remains strong. Cyclohexane was first obtained by the direct fractional distillation of suitable crude petroleum refinery streams. Now the major portion of cyclohexane is obtained from the direct hydrogenation of benzene. Conventionally the reaction is carried out in vapor or mixed phase using a fixed bed reaction. The reactor temperature is controlled to be between 350 to 500° F. Higher temperatures can lead to thermodynamic limitations on benzene conversion, thermal cracking and increased by-product. In general, the amount of byproducts in the effluent stream from a hydrogenation reactor increases with hydrogenation temperature or conversion of benzene or both.
Peterson in U.S. Pat. No. 2,373,501 discloses a liquid phase process for the hydrogenation of benzene to cyclohexane wherein a temperature differential is maintained between the top of the catalyst bed where benzene is fed and the outlet where substantially pure cyclohexane is withdrawn. The temperature differential is due to the change in the exothermic heat of reaction released as less and less benzene is converted as the concentration of benzene decreases. Specifically the top of the catalyst bed is at a higher temperature than the lower catalyst bed. Hydrogen is supplied countercurrent to the benzene/cyclohexane flow. Temperature control coils are disposed within the reactor to maintain the temperature differential if the exothermic heat of reaction is not sufficient or to cool the bed if too much heat is released. Peterson recognizes that although the bulk of his reaction takes place in the liquid phase a portion of the benzene and cyclohexane will be vaporized, especially near the top of the reactor where the benzene concentration is highest and conversion is highest. A reflux condenser is provided to condense the condensible material and return it to the reactor. Thus, a substantial portion of the heat of reaction is removed by condensation of the reactants vaporized throughout the reaction. Peterson maintains a liquid level above the topmost catalyst bed but allows room for vapors to escape to the condenser where the heat of reaction is removed.
Larkin, et al. in U.S. Pat. No. 5,189,233 disclose another liquid phase process for the hydrogenation of benzene to cyclohexane. However, Larkin, et al utilize high pressure (2500 psig) to maintain the reactants in the liquid state. In addition Larkin, et al disclose the use of progressively more active catalyst as the concentration of benzene decreases to control the temperature and unwanted side reactions.
Hui, et al. in U.S. Pat. No. 4,731,496 disclose a gas phase process for the hydrogenation of benzene to cyclohexane over a specific catalyst. The catalyst reported therein is nickel supported on a mixture of titanium dioxide and zirconium dioxide.
U.S. Pat. No. 6,750,374 discloses a process for the hydrogenation of benzene using hydrogen containing up to about 15 mole % impurities, such as carbon monoxide and light hydrocarbons with an alumina supported catalyst containing from about 15 to 35 wt. % Ni and from about 1 to 15 wt. % Cu. The catalyst may contain additional elements such as Mo, Zn, Co, Fe.